Low cost renewables trump coal

Source: BNEF

I'm not sure I understand what they mean by this: 

Battery storage systems (co-located and stand-alone) presented here have four-hour storage.  In the case of solar- and wind-plus-battery systems, the range is a combination of capacity factors and size of the battery relative to the power generating asset (25% to 100% of total installed capacity).

Given capacity factors of say 30% (they vary), 100% of installed capacity would be 3.3 hours of storage.  Storage equal to 25% of nameplate capacity would equal just one hour of wind/solar farm output.  So, I'm a bit puzzled.  Any informed reader with a better understanding than me?

At any rate, the estimates excluding storage are clear enough and are in the same range as the figures released by Snowy Hydro.  Must cheaper than coal and gas.  Plus, once built, the marginal cost of wind and solar is zero.  When supply to the grid from half hour to half hour is bid for by the grid operators, they start start with the cheapest bid and work up until projected demand is satisfied.  Wind and solar farms may as well make the lowest bids, because the equipment is there, ready to go, and must be paid for whether it is used or not.  Might as well use it.  But that takes away market share from coal.  And coal power stations can't be dialled up or down in half-hour increments.  Coal increasingly is only needed when renewables aren't producing, and that part-time usage isn't enough to keep them profitable. 

This is a problem for the grid, because the gaps created by variable renewable output must be filled, and if coal power stations close because they're unprofitable, the grid will crash.  Storage is essential.  But the bulk electricity pricing market and rules have to be changed to reward storage providers if storage is to be built.  And the regulator (AEMC) has responded sluggishly and inefficiently to the change in technology, and is dragging its heels on the regulatory and rule changes needed.  This, not cost,  is now the major constraint on getting to 100% renewables in Oz.

Note how battery storage for peaking power is now at the bottom end of the cost range compared to the alternatives.  And that's now: battery costs are falling by 20% per annum.  It's very hard to find any way that coal will recover.